With a progress of molecular biological analysis technology, it has become possible to acquire very useful information in the fields of clinical diagnosis, genetic engineering, etc by analyzing nucleic acid molecules that carry genetic information. In carrying out the analysis of the nucleic acid molecules, extraction and recovery of nucleic acid molecules are important steps. Generally, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) present as nucleic acid molecules in a biological sample; it is preferable to separate and recover the deoxyribonucleic acid and ribonucleic acid from a single sample, particularly if an available amount of the sample is limited.
In general, when extracting ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) in the biological sample such as blood, cells, tissue, etc, it is necessary to break cells and isolate nucleic acids by physical treatment with stirring, ultrasonic vibration or heating or by chemical treatment with a surfactant or protease, etc. Then, in order to recover isolated nucleic acids, a cesium chloride density gradient ultra-centrifugal separation, a phenol extraction or column chromatography separation is conducted. These methods are used singly or in combination in accordance with objective nucleic acids, samples used, or usage of nucleic acids to be extracted.
Boom et al proposed a simple method of extracting and recovering nucleic acids from a biological sample, wherein silica particles are used as a nucleic acid bonding carrier in the presence of caotropic salt (See Non-Patent Document 1, for example). According to this method, single strand nucleic acids (single strand DNA and RNA) and double strand nucleic acids (double strand DNA) are separated simultaneously. However, it is difficult to separately recover the isolated deoxyribonucleic acid and ribonucleic acid.
On the other hand, there is a method for selectively recovering ribonucleic acid from a biological sample (See Patent Document 1, for example). According to this method, an acidic solution containing a caotropic agent, a water-soluble organic solvent and a nucleic acid bonding carrier are added to a sample containing ribonucleic acid, followed by mixing the solutions. The carrier to which ribonucleic acid is bound is separated from a liquid phase, thereby to extract and recover only ribonucleic acid by eluting a composite of the ribonucleic acid and carrier composite. However, the deoxyribonucleic acid that coexists with the recovered ribonucleic acid is not recovered.
Further, a method of separating and recovering a double strand/single strand nucleic acid from the same biological sample is disclosed in Patent Document 2, for example. In this method, the double strand nucleic acid in a sample solution is bound to silica particles under proper conditions of a caotropic agent, a chelating agent, pH value, etc. Then, a concentration of the chelating agent in a supernatant from which the silica particles bound to the double strand nucleic acid are removed is changed to thereby cause binding of the single strand nucleic acid to the silica particles. As a result, the double strand nucleic acid/single strand nucleic acids are separately recovered. However, this process needs a centrifugal separation to recover the silica particles, thereby to make the method complicated.
A method of separating double strand nucleic acids and single strand nucleic acids is disclosed in Patent Document 3, for example. In this method, only the deoxyribonucleic acid, i.e. the double strand nucleic acid is bound to an inorganic carrier under a condition free from substances containing alcohol radicals to separate them from the ribonucleic acid. This method may include a step for separating the double strand nucleic acids and the single strand nucleic acids by separate elution from an inorganic carrier, after the double strand nucleic acids/single strand nucleic acids are simultaneously bound to the inorganic carrier.
However, in order to recover the double strand nucleic acids and the single strand nucleic acids, an alcoholic solution of high concentration is needed. Thus, there are problems of safety in handling and of inhibition of enzyme reaction due to alcohol remaining in the recovered product.    Patent Document 1: Japanese Patent Laid-open Hei 11-196869    Patent Document 2: Japanese Patent Re-publication 2000-505295    Patent Document 3: Japanese Patent Laid-open 2002-18797    Non-Patent Document 1: J. Clin. Microbiol. 28; 495-503(1990)
In extraction of nucleic acids by density gradient ultra-centrifugation, a nucleic acid purification processing needs a long period of time. In phenol extraction, care for safe processing must be taken because phenol i.e. a poisonous substance is used. Further, it is unavoidable to make the process complicated.
As for the above-mentioned simplified method for extracting and recovering nucleic acids, it is difficult to separate and recover ribonucleic acid and deoxyribonucleic acid using reagents that are easy to handle, as described above.